Tubes are in common use in various heat exchanger apparatuses such, for example, as boilers and condensers. The tubes employed in a boiler are commonly exposed to hostile elements such as fly ash. These hostile elements can have the effect of abrading and corroding the tubes with the result that the tubes experience early failure resulting in major maintenance and significant boiler down-time costs. Many devices have been devised to protect the tubes from the hostile elements. In one such protective device, metal sheets are hung between rows of vertical tubes and vertically arranged bars are welded to the faces of the sheets so as to maintain adjacent sheets in proper spaced relation. Whereas this arrangement has been generally effective in shielding the tubes from the hostile elements, the tube shields employing such spacer bars suffer from several disadvantages. Specifically, the bars add significantly to the cost of the tube shields both in terms of added material and in terms of added labor to weld the bars to the sheets; the bars add significantly to the weight of the shields; the welds holding the bars to the sheets ultimately fail with the result that the bars fall off and drop into the economizer bin of the boiler with consequent damage to the boiler and consequent boiler down-time to remove the bars; the shields, after the bars have fallen off, will themselves work loose from the tubes and fall downwardly into the economizer bin with consequent damage; and the bars tend to rigidify the shields to the extent that the shields are substantially inflexible and cannot be flexed or bent to facilitate installation between closely spaced tubes.